I hope what I offer helps.

I also hope that you are getting paid for all the hours you are working.

I would like to suggest you approach this in a few ways:

If you have not already, start documenting what work you have been/are doing--do this at home. Be specific in the ways another employer would be interested in, for example, that you supervised, that you analyzed, streamlined, increased (whatever the company does or values) that you saved/made money for the organization, those sorts of marketable and desirable skills.

At the same time, do what one of the other poster says and get a doctor/therapist to write up that to address your chest pain your "prescription" so to speak is to take an exercise class/rest for half a day on Saturday/whatever seems to be workable. When I was in counseling, my therapist worked with me on the sorts of things I like to do -- it is likely your doctor/therapist will too.

The reason for this is two-fold. First you do need to deal with your stress in healthful ways, and you want to have good legitimate, irrefutable ways to stop being available to work 24/7.

Also, I believe another poster suggested this: fill in your education with classes, seminars, etc to boost your knowledge in the things you are already doing with progression to a higher level so that you will be more valuable to the company. What you don't need to say is that you're really preparing for a company that will treat you better. These classes/seminars/etc should be done during some of those hours they would have you working like a dog. Ideally they will pay for them, if not, look around to see what you can find that you can afford on your own. Frankly, I think needing 10 hours a week to participate in a course being offered by Coursera.org is valid, assuming it adds to the knowledge you need for your field!

You're not alone; and it isn't just IT that mistreats/abuses/and overworks/enslaves its employees. Many places are doing it now so they can 'cheap out' and not hire the amount of staff it truly takes to run their business. They're determined to work us to death, where I work.

Lastly, learn to employ the phrase "Is there a problem with that"--and be prepared with an alternative that still is in your favor.